Posts Tagged: fuel trim
Fuel Trim: What the numbers mean
Fuel Trim Explained: What the numbers mean and how to use the data to diagnose your engine Quick Summary: Fuel trim in an OBD-II vehicle is the engine computer’s ongoing adjustment of fuel injector duration to keep the air-fuel mixture as close as possible to the ideal 14.7:1 ratio. Using feedback from the oxygen sensors, the ECM monitors whether the engine is running rich (too much fuel) or lean (too much air) and instantly alters short-term fuel trim (STFT) to correct the mixture. In contrast, long-term fuel trim (LTFT) stores … Read More
How to Use Fuel Trim Diagnostics to Solve Engine Problems
Common Causes of High Positive and Negative Fuel Trim Quick Summary Understanding fuel trim diagnostics is one of the most powerful diagnostic skills you can learn. Fuel trim data tells you whether the engine computer is adding or subtracting fuel to maintain the correct air/fuel ratio. By learning how to read fuel trim data, understanding short-term vs. long-term fuel trim, and knowing what causes positive or negative corrections, you can quickly identify vacuum leaks, fuel delivery problems, faulty MAF sensors, faulty oxygen sensors, and intake leaks. Fuel trim isn’t just … Read More
Top Causes of the P0171 Code and P0174 Code
Fix a P0171 and P0174 Lean Code Using Proven Diagnostic Strategy Quick Summary The P0171 and P0174 codes are some of the most misunderstood OBD-II trouble codes. Both codes indicate the engine is running too lean—either too much air or too little fuel. A P0171 indicates a lean condition on bank 1, while a P0174 indicates a lean condition on bank 2. Most of the time, these codes are caused by something simple, such as a vacuum leak, a dirty MAF sensor, or low fuel pressure. But I’ve also seen … Read More